The van is a 2000 SEL with about 85,000 miles.
I have changed the fluid and filter 4 times in the last 5,000 miles and still the shudder persist. It usually occurs under a mild load (going up a slight grade or slightly accelerating). I only notice it in 4th gear. It is not noticed during hard acceleration with high engine revs. Turning off the Over Drive does not stop the shudder under identical engine load conditions.
I know this jerking shudder cannot be good on the drive train. SO, WHAT IS CAUSING THIS!!!
I am using Castoil Mercon V fluid. I know they recently changed their formula to a less stinky type, but they said it was re-formulated for better performance. I would rather find out what is causing the problem rather than treat it with some aftermarket mystery oil additive.

What causes shudder?? Is the fluid getting to hot?? Is there a flow restriction?? Do I need to install an external cooler?? Is the interm servo causing this?? Could it be a sensor or electrical issue?? Is the converter bad?? Is it a design flaw??
Your thoughts please!!!

The van is a 2000 SEL with about 85,000 miles.
I have changed the fluid and filter 4 times in the last 5,000 miles and still the shudder persist. It usually occurs under a mild load (going up a slight grade or slightly accelerating). I only notice it in 4th gear. It is not noticed during hard acceleration with high engine revs. Turning off the Over Drive does not stop the shudder under identical engine load conditions.
I know this jerking shudder cannot be good on the drive train. SO, WHAT IS CAUSING THIS!!!
I am using Castoil Mercon V fluid. I know they recently changed their formula to a less stinky type, but they said it was re-formulated for better performance. I would rather find out what is causing the problem rather than treat it with some aftermarket mystery oil additive.

What causes shudder?? Is the fluid getting to hot?? Is there a flow restriction?? Do I need to install an external cooler?? Is the interm servo causing this?? Could it be a sensor or electrical issue?? Is the converter bad?? Is it a design flaw??
Your thoughts please!!!
Are you sure that it is a transmission issue? this could also (not totally sure)
a misfire issue which appears during light or medium load. Defect egr system
(not only the egr valve itself but all relate parts) can produce shudder, hesitation on light and medium load.

... also check out the harness for damage. Some '99+ units have powertrain harness damage as harness rubs against a/c tubing and other firewall protrusions. You'll have to remove the wipers and cowling to check this area.

It may be worth a trip to the dealer or tranny shop to have codes scanned. (Free scanning at AutoZone is only effectivce for powertrain codes related to emissions).

I dont belive that the converter causes shudder.

It may be the front mounting of the motor. The rubber breaks and the motor lifts up.

But certainly the 2000´der Windstars have converterproblems.....

Here´re some pics of broken rubber montings:
http://galerie.windstar-club.de/details.php?image_id=446&sessionid=5724f7a2688eeeefb1a9a2f342cc0d76